(Harrisburg) -- Pennsylvania voters have a lot of races to settle in Tuesday's primary election, including picking Republican challengers to Democratic Gov. Tom Wolf and U.S. Sen. Bob Casey.

The hotly contested gubernatorial primary has exceeded $20 million in spending and is the ballot's marquee race. The sleepier Republican contest for U.S. Senate could still play a role come November in deciding whether Republicans maintain control of the U.S. Senate.

Also on tap are contested primaries for lieutenant governor and a slew of crowded U.S. House races following Pennsylvania's court-ordered redrawing of congressional district boundaries and a host of open seats in the Legislature.

A top official with the Department of Homeland Security was in Pennsylvania on Tuesday, but said there have been no credible threats to the state's election system. Pennsylvania was one of the 21 states targeted by Russian hackers ahead of the 2016 presidential election, according to federal authorities.

The biggest threat for this election is the weather, a state official said, urging voters to cast their ballots before rain and wind sweep across the state.

Polls opened at 7 a.m. and will close at 8 p.m.

GOVERNOR

Republican voters are deciding between three candidates to challenge Democratic Gov. Tom Wolf, who is uncontested in his primary to seek a second term in November.

On the Republican ballot for the nomination are Laura Ellsworth, a commercial litigation attorney and former chairwoman of the Greater Pittsburgh Chamber of Commerce; Paul Mango, a former health care systems consultant and ex-Army paratrooper; and Scott Wagner, a state senator from York County who has made millions in the waste-hauling industry.

Both Mango and Ellsworth are first-time candidates from suburban Pittsburgh. Wagner is the party's endorsed candidate.

LIEUTENANT GOVERNOR

Lt. Gov. Mike Stack is fighting for another term in office after a first term in which he had a chilly relationship with Democratic Gov. Tom Wolf.

Stack, a former Philadelphia state senator, has four Democratic challengers.

They are Nina Ahmad, a former deputy mayor under Philadelphia Mayor Jim Kenney; Chester County Commissioner Kathi Cozzone; Montgomery County activist Ray Sosa; and John Fetterman, who is something of a national media darling for his efforts to revive the down-on-its-luck steel town of Braddock, where he is mayor.

Should Stack lose, he would become the first officeholder beaten in a primary election since Pennsylvania allowed lieutenant governors to run for a second term in the 1970s.

Four Republicans are running in the primary.

They are Jeff Bartos, a real estate investor from suburban Philadelphia; Diana Irey Vaughan, a Washington County commissioner; Kathy Coder, a Republican State Committee member from Allegheny County; and Marguerite "Peg" Luksik, a longtime conservative activist from Cambria County.

U.S. SENATE

Four-term U.S. Rep. Lou Barletta, the former mayor of Hazleton in northeastern Pennsylvania, and five-term state Rep. Jim Christiana of Beaver County are seeking the Republican nomination to challenge Democratic U.S. Sen. Bob Casey.

Casey, the son of the late former governor, is uncontested in the primary and is running for a third, six-year term.

Barletta is endorsed by the state Republican Party and backed by President Donald Trump.

U.S. HOUSE

Pennsylvania is hosting 21 contested primary elections on Tuesday's ballots for the state's 18 U.S. House seats.

Six incumbents -- Democrats Mike Doyle, of Pittsburgh, and Brendan Boyle and Dwight Evans, of Philadelphia, and Republicans Brian Fitzpatrick, of Bucks County, Tom Marino, of Lycoming County, and Lloyd Smucker, of Lancaster County -- are facing primary challenges.

Democrats are settling primary races to challenge five Republican incumbents and to run for five open seats in November's general election. Republicans are settling primary races to challenge one Democratic incumbent and to run for four open seats in November.

Haverford and Havertown are solidly Democratic areas near Philadelphia that used to be in a majority Republican congressional district but are now in a newly reshaped majority Democratic district.Eileen McCormick, a Republican, voted at Manoa Presbyterian church in Havertown for GOP candidate Pearl Kim for U.S. Congress.

"I shouldn't say this, but that was a wasted vote. That's going Democratic," she said.

Another voter at the church, Julie Nelson, said she voted for Democrat Greg Vitali in the crowded 5th district primary. She said of the political shift with redistricting: "It's about time. It's what we need."

STATE LEGISLATURE

There are dozens of primaries for 228 legislative seats on the ballot, as Republicans look to defend huge majorities in the House and the Senate.

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